Protective cable nets system (pcns)

ABSTRACT

A combined net structure is disclosed that comprises a non-planar coarse net with a grid-like structure comprising a plurality of coarse cables wherein longitudinal coarse cables intersect with latitudinal coarse cables to form a plurality of coarse cells and cutouts of a fine net attached to the coarse net, wherein the fine net comprises a plurality of adjacent fine cables. Each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points, wherein the fine net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of the fine quadrangular cells. System that comprises the combined net structures are disclosed as well.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT application No. PCT/IL2018/050181, filed on Feb. 19, 2018. The disclosure of the priority application is incorporated in its entirety herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of defense systems. More particularly, the present invention relates to a system for blocking ballistic and direct hit munitions and drones.

BACKGROUND OF THE INVENTION AND PRIOR ART

Munitions such as antitank missiles, rockets, shells, bomblets, and other artillery or explosive objects are used and often fired by army units or terrorist organizations into urban areas, critical facilities and military zones. Drones, with or without explosives, can penetrate the aerial perimeter of the mentioned areas and zones. There is a great need for protection of several specific zones from these fired objects and drones. Another example of such zones are zones that have special installations, infrastructures and arsenal.

US 2010/0102166 relates to an apparatus and method of missile interception. The missile interceptor comprises a net body with a plurality of sections and at least one missile trajectory effector, preferably an exploding ring. A missile, passing through the net body, picks up the ring, which explodes once the missile passes a sufficient distance away from the missile interceptor.

WO 2008/114261 relates to a barrier, wherein the barrier is an upwardly immobilized barrier (UIB) comprising a barrier, comprising at least one netting adapted to avoid or hinder penetration of actuated members, and at least one balloon immobilizing the netting from the nettings top portion.

US 2010/0294124 relates to a device and a method for protecting objects against rocket propelled grenades having a hollow nose cone including a netting of knotted and coated super strong fibers disposed in front of the object, in such a manner that the nose cone of a rocket caught in the netting will penetrate one of the meshes of the netting and be deformed through strangulation, thereby disabling the detonator.

Analysis of Geometrically nonlinear Structures, Second Edition, Chapter 7—CABLE NETS AND FABRIC STRUCTURES; by Robert Levy and William R. Spillers; 2003 Kluwer Academic Publishers; pages 151-186, relates to cable net structures formed by tailoring portions thereof. This publication gives the background of the calculations and design of the hereunder described invention.

The design of cable nets and fabric structures can be described in terms of three events: shape finding, analysis, and patterning. In the process of shape finding, the designer specifies a set of parameters and then computes other parameters finally resolving the details of the shape of the structure. Under analysis, loads are applied to a structure whose shape is known and the response to these loads computed. Patterning is concerned with how a curved surface is to be formed from rolls cable nets or fabric.

The process of shape finding can be thought of roughly in terms of stretching cable nets or fabric over a frame of arbitrary shape. (For example, in the skylight problem of FIG. 8A, the geometry is fixed along both crossed arches and the base.) Clearly the cable nets or fabric must follow the frame at the boundaries and certain tensions can be specified on these boundaries. But just as clearly, the locations of the cable nets or fabric points within the frame must be determined from the equations of equilibrium and in some cases the material parameters. Finding the locations of these internal points is the process of shape finding.

In the early days (Frei,1973) and in the absence of the computer, physical models were commonly used in the design of fabric structures and cable nets. It is now conventional wisdom that small-scale models are not sufficiently accurate either for the prediction of forces or the patterning of the cable nets or the fabric.

If needed to find a shape which is in equilibrium, this can be done by applying loads to, for example, a stretched elastic sheet and then using the deformed sheet or a scaled version of it as the shape. There is nothing wrong with doing so but care is required since loads applied to a sheet may introduce stress concentrations which may not be desired in the structure under design. The basic reference to this method is Argyris, et al. (1964).

Any computer program for nonlinear structural analysis can be used to achieve shape in this manner but it does not appear common to do so. Pertinent to this is the fact that the cable nets or the fabrics now commonly used in permanent structures cannot tolerate large strains without tearing.

It has been noted by Schek (1974) that if the ratio of the bar force to its length is held constant in a cable net, the associated geometry can be found by solving a system of linear equations. (A similar statement can be made for a finite element fabric model.) This approach is frequently used in the design of fabric structures.

The force density method is based on the fact that the force on the end of a truss bar can be represented by the product of the bar force and a unit vector in the direction of the bar as shown in FIG. 8AB. Here n_(i) is the unit vector of member i, F_(i) is the bar force of member i, and L_(i) is the length of member i. The components of the force vector can be written as

$\begin{matrix} {{{{\left( F_{i} \right)_{x} = {\frac{F_{i}}{L_{i}}\left( {X_{A} - X_{C}} \right)}}\left( F_{i} \right)_{y}} = {\frac{F_{i}}{L_{i}}\left( {Y_{A} - Y_{C}} \right)}}{\left( F_{i} \right)_{z} = {\frac{F_{i}}{L_{i}}\left( {Z_{A} - Z_{C}} \right)}}} & \left( {8A} \right) \end{matrix}$

Clearly, if the “force density”, F_(i)/L_(i) the ratio of the bar force to its bar length is some known constant, the force at the end of the bar becomes a linear function of the coordinates X_(A),Y_(A),Z_(A) and X_(C),Y_(C),Z_(C) at the ends of the bar. What this means is that when the equilibrium equations are written, they are linear in the node coordinates. Thus, problems can be formulated in which the node coordinates (shape) are easily found by solving a system of linear equations.

One of the shortcomings, of course, with this method is that it is usually preferable to specify the member force F_(i) rather than the force density F_(i)L_(i). In fact, L_(i) is not really known until the node coordinates have been computed by some shape finding algorithm.

As FIG. 8C indicates, similar arguments can be made for a simple membrane finite element. Roughly, given a simple finite element such as Zienkiewicz's plane stress element (Zienkiewicz, 1977) and an existing state of stress, nodal forces can be computed. (They depend upon both the state of stress and the geometry of the finite element.) These nodal forces can be expressed as linear combinations of the unit vectors n and m (FIG. 8C) which describe the slopes of two sides of the finite element. As was done for the bar, these unit vectors can be factored into a term linear in the node coordinates and whatever remains. Obviously, when the coefficients of these linear terms are specified as in the case of the bar, the equilibrium equations become linear in the coordinates of the elements.

Siev and Eidelman (1964) showed that if equilibrium is satisfied over a grid in the horizontal plane (see FIG. 8D), vertical equilibrium can be used to compute the elevation (shape) at the grid points. This is probably the most simple way to find shape and will be discussed at some length below.

The grid method is probably the most simple way to find shape. It requires, first of all, a grid in the horizontal plane but any numerical method for finding shape requires some kind of a grid of points. Member forces must be assumed or determined so that the cable net or finite element system is in equilibrium in the horizontal plane, but this too can be a trivial step. That is clearly the case in the simple example of FIG. 8F where it is assumed that the horizontal cable force components are all 1,000 lbs. (Constant force components over a rectangular grid are clearly in equilibrium in the horizontal plane.) If only the rise of the circular arches has been specified, it is also required to compute the elevations of the points of attachment along these arches as is done below. The final step is to write the equations of equilibrium in the vertical direction and then solve a system of linear equations for the unknown elevations at these points. Following are two examples of shape finding using the grid method.

This example is a piece (type B in FIG. 8E) of a cross arched skylight of dimensions 20 ft×40 ft. Since the base of this skylight is not square, it would be necessary to find the shape of another piece (type A in FIG. 8E) to complete its design.

The piece of skylight is taken as a 9-member cable net laid over a right angled triangular structural base having two edges of 10 ft and 20 ft as shown in FIG. 8F. It is supported at nodes 4,5,6 by the third edge which is a circular arch having a rise of 5 ft. With horizontal force components of 1,000 lbs in each of the cables it is required to find the vertical coordinates of nodes 1,2,3 so that equilibrium is maintained.

The elevations of nodes 5 and 6 are first established from the arch geometry. The radius of the arch is obtained from:

${{\theta = {{2 \times {\arctan \left( \frac{5}{2{2.3}607} \right)}} = {2{5.2}087^{\circ}}}}R} = {\frac{2{2.3}607}{\sin 25.2087{^\circ}} = {5{2.5}00\mspace{14mu} {{ft}.}}}$

Now using the equation fora circle, x²+y²=R², the z-coordinates of nodes 5 and 6 are obtained as described in FIG. 8F

z ₅=√{square root over (R ²−7.453²)}−R cos θ=4.4682 ft

z ₆=√{square root over (R ²−14.907²)}−R cos θ=2.8391 ft

The next step is to write vertical joint equilibrium for each free joint by adding the contribution of each member. (Remember that the grid method starts with the satisfaction of equilibrium in the horizontal plane.) The simple relation of FIG. 8D is used for that purpose, i.e.

$\begin{matrix} {V = {\frac{H}{L_{H}}\left( {Z_{A} - Z_{C}} \right)}} & \left( {8B} \right) \end{matrix}$

-   -   Here H=1,000 lbs and L_(H) has only two values which are ΔY=3333         ft and ΔX=6.667 ft. Considering vertical equilibrium:

${{node}\mspace{14mu} 1\text{:}\mspace{14mu} {H\left( {\frac{5 - z_{1}}{\Delta \; X} + {2 \times \frac{4.468 - z_{1}}{\Delta \; Y}} - \frac{z_{1} - z_{2}}{\Delta \; X}} \right)}} = 0$ ${{node}\mspace{14mu} 2\text{:}\mspace{14mu} {H\left( {\frac{z_{1} - z_{2}}{\Delta X} + {2 \times \frac{z_{3} - z_{2}}{\Delta \; Y}} - \frac{z_{2}}{\Delta X}} \right)}} = 0$ ${{node}\mspace{14mu} 3\text{:}\mspace{14mu} {H\left( {\frac{{{2.8}39} - z_{3}}{\Delta \; Y} + \frac{{{4.4}68} - z_{3}}{\Delta X} - \frac{z_{3} - z_{2}}{\Delta y} - \frac{z_{3}}{\Delta X}} \right)}} = 0$

-   -   Observing that ΔX/ΔY=² and canceling H the above equations are         rewritten and solved as

−6z ₁ +z ₂+22.872=0

z ₁−6z ₂+4z ₃=0

2z ₂−6z ₃+10.146=0

-   -   Substituting z₂ from the first equation and z₃ from the third         equation into the second equation yields

${z_{1} - {6\left( {{{- 2}{2.8}72} + {6z_{1}}} \right)} + {4\left( \frac{{1{0.1}46} + {2\left( {{{- 2}{2.8}72} + {6z_{1}}} \right)}}{6} \right)}} = 0$

-   -   ⇒−27z₁+113.5=0 ⇒z₁=4.203 ft and z₂=2.350 ft; z₃=2.474 ft. This         completes the example since an initial shape in equilibrium has         been found.

The next example, which is described by FIGS. 8G and 8H, is in fact the skylight of FIG. 8A is also referred as DOME in FIG. 8P. FIG. 8I shows a node map of ⅛ of this structure which is all that it is required for design due to symmetry.

Following are the calculations which are necessary to determine the elevations of the fixed points on the arch (nodes 5, 9, 12, 14 and 15) having a specified rise of 30 inches. Here the base of the skylight is 172 inches square, and the cables are equally spaced in the horizontal plane. The elevations z₅ and Z₁₅ are given as 30 inches and 0 inches respectively. The angle θ and the radius of the arch are obtained as

${\frac{\theta}{2} = {{\tan^{- 1}\frac{3.0}{121.622}} = {\left. {1{3.8}56^{\circ}}\Rightarrow\theta \right. = {2{7.7}125^{\circ}}}}}{{R\sin \theta} = {\left. {12{1.6}22}\Rightarrow R \right. = {26{1.5}33\mspace{14mu} {in}}}}$

Once the shape has been determined the final cable forces can be computed as indicated in FIG. 8I (1).

Having obtained a shape using in this case the grid method, it is natural to hope that a better shape perhaps close to the given shape might be obtained. For example, there are many reasons such as efficiency in the use of material to look for a shape in which the bar forces or the membrane stresses or cable forces are constant.

When such a shape exists, it may be possible to generate it using a nonlinear structural analysis computer program. This is the idea of “smoothing” which has been described by Haber and Abel (1982). There are two steps to the smoothing procedure:

1) The output of the shape finding program is used as input to the nonlinear analysis program except that the desired cable forces, here taken to be 1,000 lbs rather than the computed cable forces are used. Clearly this initial configuration is not in equilibrium.

2) A fictitious, small value of E, Young's modulus, is used during the subsequent analysis. This essentially disables the elastic stiffness matrix and prevents the cable forces from changing. When the nonlinear analysis converges, a shape has been obtained for which the cable forces are constant. In this case the cables have moved to form geodesics in the surface of the structure.

FIGS. 8J-8K show a cable net which looks something like a hyperbolic paraboloid; it is supported at four points and bounded by four edge cables on four sides. This structure is more complex than the example above because of its four edge cables. A node map has been created and displayed in FIG. 8L. (Note that cable node 15, which defines the “sag” of the edge cable has been forced to lie on a grid point.)

In order to get started with the grid method in this case it is first necessary to go off and solve the (horizontal) cable problem by hand. FIG. 8L is a free body diagram of half of one edge cable. Symmetry requires that the force components at the exposed end be equal. Moment equilibrium then provides R (see below) after which individual cable forces and reactions may be calculated using force equilibrium starting with cable 32 and moving upwards up to cable 29. Following are the required calculations:

Σ moments about top⇒1000×2+1000×4+1000×6+1000×2+R×4−R×6=0 ⇒14000=2R⇒R=7000.

force in cable 32 is √{square root over (6000²+7000²)}=9219 lbs

force in cable 31 is √{square root over (5000²+7000²)}=8602 lbs

force in cable 30 is √{square root over (5000²+8000²)}=9433 lbs

force in cable 29 is √{square root over (4000²+8000²)}=8944 lbs

In the final design (FIG. 8M) the interior cable forces are of course not constant. Smoothing can be used to determine a shape with constant internal cable forces but in this case the real stiffness of the edge cable must be used if the plan shape of this structure is to be preserved.

The final step in the design of cable nets or fabric structures is patterning. Fabric structures are usually made by joining strips of fabric which have been cut from rolls of cloth.

The object of the design process is to produce a structure which will assume a specified shape when it is prestressed. This implies that cables, for example, must be fabricated “too short” so that they will fit together when prestressed. Similarly, there is a step-in patterning called “compensation” in which the stretch of the material under prestress is introduced into the patterning process. That step can be easily appended to the end of the patterning process

The basic problem of patterning is the construction of a curved surface out of flat pieces of material. This can be done in the following manner. First, the surface must be “triangulated”. This is the process by which the curved surface of the structure is approximated by a collection of flat triangular facets. It is usually done during the analysis phase of fabric structure design in order to deal with, for example, environmental loads. The next step is to select “strips” of triangles over the structure. These strips must cover the structure and must be SERIALLY connected. The point is that strips of serially connected triangles can be deformed into a flat sheet without stretching. A patterning for the two examples discussed above is described in FIGS. 8N and 8O.

To produce “patterns” from which fabric or cable nets are cut, grid points from the shape finding stage are taken. It could as well have been done using points interpolated over the shape. Here actual dimensions are created so that material strips of fabric or cable nets can be cut from rolls of flat fabric or cable nets.

Given a physical “strip” across a structural surface, this strip may be described by listing a sequence of nodes as indicated in FIG. 8P. In this sequence points 1 and 6 define a starting line; each additional node defines a triangle which is serially connected to the preceding one by using the line formed by the new node and the second node in the sequence back from it.

The “fan strip” of FIG. 8P indicates a configuration in which this description does not work. In this case triangle 37-24-23 requires going back in the strip sequence 3 rather than 2 nodes. That fact is indicated by assigning a negative sign to node 24 in the strip sequence.

A three-dimensional description of a strip is now in place. The projection of this representation onto a plane can be done in the following manner. The orientation of the first edge (edge 1-6 from DOME above) of the strip on the plane is arbitrary. In a typical step, a new node (eg. node 2) describes a new triangle in space one side of which is the line from the last node to the new one. The real three-dimensional angle between the last two lines defined on the strip in then computed using the scalar product of unit vectors which describe the slopes of these lines. This angle allows the next point to be located on the plane projection of the strip. When all the points have been projected onto the plane, the strip is rotated so that it will lie within a piece of fabric of minimum width. Finally, suitable coordinates for the strip which are convenient for cutting are printed out.

With regard to programming details, PATTERN.FOR begins with some now familiar input and then produces a plot showing the length of lines in the surface to be patterned. This plot can be useful when checking patterns. Its primary do loop, (DO 11 I=1, NSTR), produces the patterning information for each strip. It begins by laying out arbitrarily the first line in the strip as described above. In the typical step, which begins with the statement 1200 IP=IABS(LIST(J+1), it constructs the unit vector which describes the slope of one side of the new triangle. It then computes the real three-dimensional angle between itself and the last triangle. This allows a new point to be projected onto the plane of the fabric.

After all points of the strip have been projected onto the fabric plane, the entire strip is rotated so that it can be contained within a piece of fabric/cablenet strip of minimum width.

However, prior art methods do not provide efficient means for blocking munitions, drones, and the like, at required zones.

It is therefore an object of the present invention to provide a method and means for blocking munitions from exploding in specific zones and drones' penetration and explosion.

It is a further object of the present invention to provide a method and means for causing the munitions to explode and capturing a penetrating drone at a safe distance from a required zone, thus protecting said zone from destructive damage and casualties.

Other objects and advantages of the present invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

The present invention relates to a system for protecting certain zones by blocking munitions from exploding in the specific zones. The present invention further provides means for preventing drones or other explosive items from penetrating into and/or exploding in said zones.

The present invention relates to a coarse net connected to cutouts of a fine net creating a light weight combined net structure that is easy to put up in place for its protective purpose. The combined net structure is foldable and easily transportable. When put in place, the combined net structure preferably has a 3-dimensional shape and is strong and can remain in shape when put up.

The present invention relates to a combined net structure comprising:

-   -   a. a non-planar coarse net with a grid-like structure comprising         a plurality of coarse cables wherein longitudinal coarse cables         intersect with latitudinal coarse cables to form a plurality of         coarse cells;     -   b. cutouts of a fine net attached to said coarse net, wherein         said fine net comprises a plurality of adjacent fine cables;

wherein each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points; wherein the fine net is spread out such that said fine cables form a series of quadrangular cells, wherein said fine net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of said fine quadrangular cells.

Preferably, each fine net cutout is substantially coextensive in shape with one or more coarse cells.

Preferably, all the coarse cells are attached to fine net cutouts.

Preferably, the fine net cutouts are connected to the coarse net such that portions of a fine cable of said fine net cutouts are attached to corresponding portions of a coarse cable of the coarse net by means of connecting elements that hold said fine cable and said coarse cable together.

Preferably, the connecting elements that hold the fine cable and the coarse cable together are flat steel pieces bent into a cylindrical shape.

Preferably, the coarse net further comprises connecting elements that connect the intersecting longitudinal coarse cables with the latitudinal coarse cables at the intersecting points.

Preferably, the connecting elements are flat steel pieces bent into a cylindrical shape.

Preferably, the fine net attachment points comprise connecting elements which are pressed cylindrical steel rings.

Preferably, the fine net attachment points comprise connecting elements which are flat steel pieces bent into a cylindrical shape.

Preferably, the fine net substantially quadrangular cells are square or rhombic cells.

Preferably, the distances between two adjacent attachment points of two adjacent non-edge fine cables are substantially the same; and wherein the imaginary line which bisects and is perpendicular to the imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables passes through an attachment point of one of said two adjacent non-edge fine cables with its other adjacent fine cable.

Preferably, the combined net structure further comprises one or more edge cables attached to the perimeter of the coarse net.

Preferably, the diameter of the edge cables is between 15 mm and 25 mm.

Preferably, the diameter of the coarse cables is between 5 mm and 10 mm.

Preferably, the diameter of the fine cables is between 3 mm and 6 mm.

Preferably, the square or rhombic cell diagonals are between 20 mm and 50 mm.

Preferably, the longitudinal coarse cables and the latitudinal coarse cables have predetermined lengths and are attached to each other at pre-calculated locations marked along their lengths.

Preferably, the predetermined lengths are such that the coarse net formed comprises a 3dimensional structure.

Preferably, an imaginary line connecting two adjacent attachment points of two adjacent nonedged fine cables is parallel to the longitudinal coarse cables or to the latitudinal coarse cables.

The present invention relates to a system comprising:

-   -   a. at least one column;     -   b. the combined net structure as explained herein;     -   c. plurality of anchors; wherein the net is attached to said         column and to said plurality of anchors.

Preferably, the combined net structure is quadrangular and one of its vertices is attached to the column, and wherein said system comprises three anchors and three vertices of said combined net structure are each attached to one of said anchors.

Preferably, the column is height adjustable.

Preferably, the anchors are concrete blocks.

Preferably, the system comprises one or more additional combined net structures as explained herein.

wherein the one or more additional combined net structures are attached to the column and to the plurality of anchors.

Preferably, the one or more additional combined net structures are quadrangular; wherein one of the one or more additional combined net structure vertices is attached to the column and the other one or more additional combined net structure vertices are attached to the anchors.

Preferably, the system comprises two columns and two anchors;

wherein the combined net structure is quadrangular comprising a first vertex, a second vertex, a third vertex and a fourth vertex; wherein said first vertex is attached to a first column, and said second vertex is opposite to said first vertex and is attached to a second column, and wherein said third vertex and fourth vertex are each attached to one of said two anchors.

Preferably, the system further comprises one or more additional quadrangular combined net structures, two columns and two anchors;

wherein each of said one or more additional combined net structures is quadrangular and comprises a first vertex, a second vertex, a third vertex and a fourth vertex; wherein the one or more additional quadrangular combined net structures first vertex is attached to the column; and wherein the one or more additional quadrangular combined net structures second vertex is opposite to said first vertex and is attached to a second column; and wherein said third vertex and fourth vertex of said one or more additional quadrangular combined net structures are each attached to one of said two anchors.

The present invention relates to a system comprising:

-   -   a. two intersecting arc structures;     -   b. a combined net structure as explained herein; wherein the         combined net structure is spread over said two intersecting arc         structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example in the accompanying drawings, in which similar references consistently indicate similar elements and in which:

FIG. 1A illustrates an embodiment of the fine net of the present invention.

FIGS. 1B-1C illustrate an embodiment of the construction of the fine net of the present invention.

FIG. 2A illustrates an embodiment of groups of cells of the coarse net of the present invention.

FIG. 2B illustrates an embodiment of cutouts of the fine net of the present invention.

FIG. 2C illustrates an embodiment of groups of cells of the combined net of the present invention.

FIGS. 3A-3B illustrate an embodiment of the one column system of the present invention.

FIGS. 4A-4B illustrate an embodiment of the one column system of the present invention.

FIGS. 5A-5B illustrate an embodiment of the two column system of the present invention.

FIGS. 6A-6B illustrate an embodiment of the intersecting arcs system of the present invention.

FIGS. 7A-7B illustrate examples of the flat steel pieces used according to an embodiment of the present invention.

FIG. 8A Prior art—Skylight example: crossed circular arches on structural frame.

FIG. 8B Prior art—The force density method for a bar element.

FIG. 8C Prior art—FORCE DENSITY METHOD FOR A MEMBRANE ELEMENT.

FIG. 8D Prior art—THE GRID METHOD.

FIG. 8E Prior art—RECTANGULAR SKYLIGHT.

FIG. 8F Prior art —A SIMPLE CABLE NET.

FIG. 8G-FIG. 8H Prior art—SKYLIGHT DIMENSIONS FOR EXAMPLE 8B

FIG. 8I Prior art—COMPUTED PRESTRESS ON ⅛ SKYLIGHT STRUCTURE.

FIG. 8I(1) Prior art—COMPUTED FINAL CABLE FORCES

FIG. 8J Prior art—(a) PLAN OF THE ‘HYPERBOLIC PARABOLOID’ CABLE NET.

FIG. 8K Prior art —(B) SCHEMATIC OF THE HYPERBOLIC PARABOLOID CABLE NET.

FIG. 8L Prior art—EDGE CABLE FOR THE HYPERBOLIC PARABOLOID CABLE NET.

FIG. 8M Prior art—NODE MAP FOR THE HYPERBOLIC PARABOLOID.

FIG. 8N Prior art—PATTERNING STRIPS FOR THE ⅛ SKYLIGHT EXAMPLE.

FIG. 8O Prior art—PATTERNING STRIPS FOR ¼ HYPERBOLIC ARABOLOID.

FIG. 8P Prior art—NUMERICAL DESCRIPTIONS OF STRIPS.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a protective cable net system (PCNS) for preventing anti-tank missiles, rockets, bomblets, shells and other artillery or aerial ammunition and drones, with or without explosive, from causing fatalities and destruction at required areas.

The strength calculation, geometrical prediction and patterning into shape of the protective cable net system, comprised of both a coarse net structure and a fine net structure, is new and inventive and in view of solid geometrically nonlinear structural theory as depicted in the aforementioned book of Levy and Spillers, 2003.

The present invention Protective Cable Nets System (PCNS) is a tensile structure which is light weight, erectable, ready to use, easy to repair, easy to transport, foldable and movable system that can protect required zones against direct hits of munitions such as missiles, rockets, shells, mortars, cluster bombs, anti-tank missiles, and other artillery or explosive objects. The PCNS can also protect required areas from small and mid-sized drones. Because of its lightweight and excessive strength the PCNS can cover large areas.

The structure of the PCNS can initiate the munitions with frontal super quick (SQ) fuses or the first fuse of double sequential warheads (the second warhead may be initiated by an additional internal net) at a safe distance from vulnerable areas such as school yards, residential houses, critical infrastructures, hazardous materials, ammunition storage, military bases, radar and antennae facilities, open grounds for troop gathering, military vehicles and aircrafts. The munitions explosion is caused on impact with the PCNS. The PCNS can withstand multiple hits of munitions with super quick (SQ) fuses, bomblet hits (exploded or unexploded), and can stop small and mid-sized drones due to its configuration, structural strength and redundancy (as will be explained hereinbelow).

The PCNS can be erected in populated areas, power and other facilities, or military zones. In populated areas or facilities where structures are in existence some of the PCNS supports may be the structural elements themselves such as reinforced concrete columns and plates. For example, when protecting military base yards, the existing buildings can act as anchors. Normally, one or two PCNS columns per module will be vertical on base plates, stabilized by oblique steel cables (preferably four per column for net redundancy) anchored to massive concrete units or fixed foundations. The net may be erected horizontally, vertically or slanted. When existing buildings provide four anchors, with one anchor being at a feasible different elevation than the other three, no additional columns will be necessary for that particular PCNS.

In military zones where structures or heavy and stable military vehicles exist some of the PCNS supports may be anchored to the structural elements or the vehicles.

The PCNS can therefore be used for:

-   1. Overhead protection against ballistic munition hits and small and     mid-sized drones. -   2. Side direct hits protection against anti-tank missiles, rocket     propelled grenades, and other direct hit explosive munitions such as     artillery shells. -   3. For camouflage with fabric of visual and multispectral nature.

According to an embodiment of the present invention, the present invention relates to a fine net comprising a plurality of fine cables (see FIGS. 1A-1C). The fine net is constructed as follows. Each fine cable is attached to two adjacent fine cables on each of its sides (with exception to the fine cables at the net edges which are attached to only one fine cable). Each fine cable (e.g. cable no. 1) is attached to its adjacent fine cables, 2 and 3, at a plurality of locations along their lengths, wherein the distance of one attachment point to its adjacent other attachment point (on the same two cables) is substantially the same distance along the whole length of the fine cable (e.g. attachment points 4 and 5). Each fine cable 1 is attached to its first adjacent fine cable 2 at a plurality of locations along their lengths (points 5) and to its second adjacent fine cable 3 at a plurality of locations (points 4), substantially being equally in between the lengths between the attachment points (5), with the first fine cable. The net is then spread out (FIG. 1A and FIG. 1C) in a manner such that the fine cables form a series of square or rhombic cells. The attachment points (of the spread-out fine net) are such that the square or rhombic cell diagonal is usually between 20 mm and 50 mm.

FIG. 1A illustrates a portion of a fine net 10. The fine net 10 comprises a cable 1 connected to cable 2 (being on its left side) at a plurality of attachment locations 5. The distances between two adjacent attachment locations 5 of cables 1 and 2 are equal, i.e. the diagonal (of the quadrangle formed between the attachment locations 5) distances are equal and the sum of the two continuous sides of the quadrangle formed between the attachment locations 5 (from cable 1 and 2) are equal. Cable 1 is also connected to cable 3 (being on its right side) at a plurality of attachment locations 4. The distances between two adjacent attachment locations 4 of cables 1 and 3 are equal, i.e. the diagonal (of the quadrangle formed between the attachment locations 4) distances are equal and the sum of the two continuous sides of the quadrangle formed between the attachment locations 4 (from cable 1 and 3) are equal. The imaginary line connecting attachment locations 5 is parallel to the imaginary line connecting attachment locations 4. The imaginary line which bisects and is perpendicular to the section connecting two adjacent attachment locations 5 passes through one of attachment locations 4.

The fine cables are preferably made of a material selected from the group consisting of steel, high strength steel, stainless steel, Fiber reinforced plastics, or Fiber reinforced polymers (FRP). The diameter of the fine cables is usually between 3 mm and 6 mm.

The fine cables are attached at the aforementioned attachment points by pre-threading pairs of cables through cylindrical steel rings and pressing the rings. The rings usually have a thickness of between 0.8 mm and 2 mm. The width of each ring is usually between 5 mm and 12 mm.

An alternate method for attaching the fine cables of the aforementioned attachment points is by pressing and bending a flat steel piece into a cylindrical shape that holds the two cables together. The flat steel pieces usually have a thickness of between 0.8 mm and 2 mm. The width of the flat steel pieces is usually between 5 mm and 12 mm. The length of the flat steel pieces is usually between 18 mm and 36 mm. According to a preferred embodiment of the present invention, an example of the flat steel piece used in the present invention, is as found in the catalog of Carl Stahl Gmbh of 2006 on page 139, e.g. the embodiments in photos “a” and “b” (shown in FIGS. 7A and 7B respectively). It should be noted that other attachment elements/connecting elements may also be used.

The fine net is constructed such that its total spread out net length is usually between 10 m and 20 m. Its total spread out net width is usually between 1.5 m and 3.0 m.

FIG. 1B shows the construction of the fine net. At the first step, pluralities of pairs of parallel individual cables (e.g. of 50 meters) are spaced apart and in parallel to one another, close to one another. One steel cylindrical ring of a first group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the first group of rings) are positioned along a first imaginary line 100.

At the second step, other than the net outmost cables, the other cables (herein also referred to as non-edge fine cables) are paired consecutively such that each right cable of the former pairs of cables is paired and bonded to the left cable of its former adjacent pair (from its right side). One steel cylindrical ring of a second group of rings is threaded through each new pair, bonding the new pair cables together, each new pair having a new left cable and a new right cable. The bonding rings (of the second group of rings) are positioned along a second imaginary line 200.

At the third step, the cables (including the net outmost cables) are paired according to the pairing in step 1. One steel cylindrical ring of a third group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the third group of rings) are positioned along a third imaginary line 300.

At the fourth step, the cables (excluding the net outmost cables) are paired according to the pairing in step 2. One steel cylindrical ring of a fourth group of rings is threaded through each pair, bonding the pair cables together, each pair having a left cable and a right cable. The bonding rings (of the fourth group of rings) are positioned along a fourth imaginary line 400. This process is continued etc., Mutatis Mutandis, wherein if the step number is odd the cable pairs of that step are according to step 1, and if the step number is even the cable pairs of that step are according to step 2. The process continues until the net length is exhausted.

The distances between imaginary ring lines 100 and 200, 300 and 400 etc. are equal. The result is a net of given width which is opened and rolled ready for transport. An alternate method for attaching the fine cables is by pressing and bending flat steel pieces (instead of the rings) into cylindrical shapes that hold the cables together.

The present invention further comprises a predesigned and pre-calculated 3-dimensional coarse net comprising a plurality of coarse cables forming a coarse net structure. The coarse net is then connected to a fine net structure comprised of corresponding predesigned and precalculated cutouts. Examples of coarse nets that may be used appear in Levy and Spillers, 2003 and described hereinabove. Both the coarse net structure and the fine net structure are independent in the structural sense and are safe and stable to carry loads.

The coarse net structure comprises a plurality of coarse cables in the form of an array of (typically approximately straight on the longitudinal axis) longitudinal coarse cables intersecting with latitudinal coarse cables, such that the intersection of the longitudinal and latitudinal cables creates a series of quadrangular cells, wherein each cell is bounded by the intersecting coarse cables. The angles of the quadrangular cells may vary for different coarse nets. The longitudinal coarse cables and the latitudinal coarse cables have predetermined lengths and are attached to each other at pre-calculated locations marked along their lengths to result in a net of coarse cables forming a series of quadrilateral cells. It should be noted that the term “intersecting” is used herein as lying across, i.e. the longitudinal coarse cables lie across the latitudinal coarse cables (write above/beneath them and touching them) forming contacting points at the intersections.

According to a most preferred embodiment of the present invention the coarse cables are connected to each other (after a pre-calculation) in a manner such that the quadrangular cells formed have a non-planar curved surface. The projection of the non-planar 3-Dimensional cells is a quadrangle. The plurality of the non-planar 3-Dimensional cells together form a 3dimensional coarse net. This is achieved by the predetermined lengths and pre-calculated locations of connection (i.e. attachment points) between the longitudinal and latitudinal coarse cables. The structure of this embodiment is such that a segment of a certain coarse cable between two attachment points is not coplanar with the attachment points forming an arc-like connection between the attachment points, and thus provides the 3-dimensional effect. A plurality of such segments between attachment points enable to form the desired 3dimensional shape of the coarse net.

It should be understood that the general directions of the intersecting coarse cables remain latitudinal and longitudinal, only with an arc-like non-planar curve between the connection points. Therefore, the general cell shapes formed between the intersecting cables remain, but the segments connecting between the vertices of the cells are not coplanar with the vertices, forming an arc-like connection between the vertices. Therefore, it should be understood that the term “substantially quadrangular cells” may also mean cells with the segments connecting between the vertices of the cells, being not coplanar with the vertices forming an arc-like connection between the vertices.

The segments of the coarse cells connecting between the vertices of the coarse cells are usually between 250 and 1000 mm.

The coarse net preferably comprises steel edge cables (preferably of 15 mm to 25 mm in diameter) attached to the perimeter of the coarse net at predesigned edge locations obtaining a 3-dimensional coarse net structure. Thus, the cells at the periphery of the coarse net (the peripheral coarse cells) may not be quadrangular. The edge cables may be connected at the edge intersecting points or to an edge of a coarse cable.

The spread-out coarse net structure forms a 3-dimensional structure with a net having longitudinal and latitudinal members that intersect forming the cells. The attachment points are such that the projection of the 3-dimensional coarse net structure may be a grid of quadrangular cells. The coarse net structure (e.g. predesigned pre-calculated contact locations between the longitudinal and latitudinal cables) may form a curved 3-D structure, as explained in Levy and Spillers, 2003 and described above.

The coarse cables are preferably made of a material selected from the group consisting of steel, stainless steel, and high strength steel used for prestressing. The diameters of the coarse cables are usually between 5 mm and 10 mm.

The coarse cables are attached at the aforementioned attachment points (intersecting points) pre-calculated in order to form the 3-D structure. The intersecting coarse cables are attached by means of attachment elements/connecting elements. According to a preferred embodiment the attachment is carried out by pressing and bending a flat steel piece into a cylindrical shape that holds the two cables together. The flat steel pieces usually have a thickness of between 1.0 mm and 3.0 mm. The width of the flat steel pieces is usually between 8 mm and 15 mm. The length of the flat steel pieces is usually between 30 mm and 60 mm. The flat steel piece structure may be similar as the flat steel piece explained hereinabove with the proper size to fit the coarse cables.

The coarse net is manufactured by marking the intersection points on the coarse cables according to a predesign and pre-calculations and pressing and bending flat steel pieces into cylindrical shapes that hold the cables together. Intersection points between edge cables and coarse cables are also marked and connections are similarly made.

The fine net structure is then attached to the coarse structure forming a combined net structure. A portion of the course net is attached to a coextensive congruent cutout portion of the fine net. The fine net comprises a set of predesigned and pre-calculated cutouts substantially coextensive and congruent in shape with one or more cells of the coarse net. An example of fine net cutouts can be shown in FIG. 2B —the cutouts being portions C1, C2, C3, C4 and C5. Incidentally, if the fine net cut outs would have been connected together they would form a 3-dimesional structure of exact geometry as the coarse net structure but will lack the benefits of redundancy, strength, resilience, ease of repair etc.

The combined net is completed by attaching cutouts of the fine net structure onto the coarse net structure cutout by cutout. Each fine net cutout is connected to its corresponding coarse net portion overlapping thereon. FIG. 2A for illustration purposes in order to understand the present invention, shows groups of cells D1, D2, D3, D4 and D5 (apart from each other) of the coarse net corresponding to the fine net cutouts, wherein actually the coarse net is one connected structure (wherein the longitudinal cables shown adjacent to each other between each group of cells are actually the same cable, i.e. one vertical edge cable, serves two adjacent cutouts). The group of coarse cells shown form one quarter of a square coarse net structure when attached. The fine net cut outs are attached to the coarse net corresponding portions (the coarse net cutouts covered with tailored fine nets), as shown in FIG. 2C being combined portions E1, E2, E3, E4 and E5.

The combined net structure is constructed by attaching portions of the fine net cutouts to the coarse cables by means of connecting elements. According to a preferred embodiment the attachment is carried out by pressing and bending flat steel pieces into cylindrical shaped binding elements (connecting elements) that hold the cables together. The fine net cutouts are connected to the coarse cables at certain locations along the coarse cables wherein the fine net is connected at a portion of a fine cable of the fine net cutouts (or by connecting a connecting element of the fine net to the coarse cables).

According to a preferred embodiment of the combined net, the fine net is arranged such that its quadrangular cells are square or rhombic cells, and an imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables is parallel to the coarse net longitudinal (or latitudinal) cables.

The combined net structure, in the structural engineering sense, is now comprised of two nets, the coarse net structure and the fine net structure. Both are stable and able to withstand loads independently. This implies that the fine net structure alone could act as a protective cable net system but will, of course, lack the benefits of redundancy, ease of repair etc.

The present invention relates to a system comprising erectable columns. According to a preferred embodiment the columns are segmental and height adjustable. The columns preferably comprise lightweight steel or composite material and preferably have a circular cross section. The column is configured to be adjusted at different heights. The column segments are pre-connected at the site into one whole piece and lifted into position by an electric or mechanical winch. Optionally the column is a telescopic column.

FIGS. 3A and 3B illustrate a small model similar to the present invention system. According to one embodiment, the combined net structure 20 comprises a coarse net structure 20 f to which is attached a fine net structure 20 e and is quadrangle and one of its vertices 20 a is connected to the column 30. The other three vertices 20 b, 20 c and 20 d are connected to anchors 35 (e.g. by means of cables). The anchors 35 can be attached to the ground or to heavy weight and stable objects such as tanks, buildings or heavy concrete blocks. According to one embodiment the net is attached to anchors which are concrete blocks. FIG. 3B shows a top view of FIG. 3A. The system with the combined net structure with the supports (e.g. anchors and column) is referred to herein as the PCNS (Protective Cable Net Structure).

FIG. 4A illustrates a drawing of a similar PCNS system comprising a quadrangle combined net 20 structure and one of its vertices 20 a is connected to the column 30. The other three vertices 20 b, 20 c and 20 d are connected to anchors 35. The column 30 is supported by anchored steel cables 40 connected (e.g. tied) to the column 30, wherein the anchored steel cables 40 are tensioned during erection. A portion of the secure zone 50 securing from the flying explosive objects or drones is also indicated.

FIG. 4B shows a top view of the PCNS drawing of FIG. 4A, with an enlargement portion showing a cutout 21 of the combined net structure 20. This cutout 21 is shown in FIG. 2C and identified as E3.

FIG. 5A shows a small model of a PCNS embodiment of the present invention, wherein the system comprises a quadrangle (preferably square) combined net structure 120 wherein one of its vertices 120 a is connected to a first column 130 a, and its opposite diagonal vertex 120 b is connected to a second column 130 b. The other vertices 120 c and 120 c 1 (at the other two opposite diagonal vertices) are connected to anchors 135. The columns 130 a and 130 b are supported by anchored steel cables 140 connected (e.g. tied) to the columns 130 a and 130 b and connected to the ground, wherein the anchored steel cables 140 are tensioned during erection. In this specific embodiment the anchored steel cables 140 are connected to the top of the columns 130 a and 130 b. In the preferable setup two sets of cables per column are specified. FIG. 5B shows a top view of FIG. 5A. The fine net, which is connected to the coarse net, is not shown in these figures.

FIGS. 6A and 6B show a small model of an embodiment of the present invention with a combined net 220 spread over two rigid intersecting arcs 230 (in this sense the intersecting may also mean intersecting on the same plane). Both models (FIGS. 5A, 5B and 6A, 6B) show coarse net structures only, wherein obviously, cutouts of fine net straps are tailored to the coarse nets forming the combined net structure.

According to an embodiment of the present invention, the system comprises a single or double layered structure. For the double layered structure an additional combined net is placed under the first combined net. In relation to the embodiment of FIGS. 3A-3B (and 4A4B) the system comprises an additional quadrangular combined net substantially identical to net 20. One vertex of the additional (second) combined net is connected to the column 30 at a location beneath (preferably 0.5 m) where the first net is attached to the column 30 (this embodiment not shown). The other vertices not attached to the column 30 are attached to the anchors 35. Optionally, the two combined nets are arranged such that they are substantially parallel to one another.

The double layered structures are advantageous when double fuse munitions are used, or when there is a need to capture some of the munition or the drone fragments. If the fired double fuse munitions do not explode on impact with the first net, they can explode on impact with the second net. In addition, the second net is also advantageous with one fuse munitions or drones by that it captures large fragments and blocks them from entering the secure zone.

With regard to FIGS. 5A-5B, the present embodiment comprises the structural features of this embodiment with the addition of the following feature. The system comprises an additional second quadrangle combined net beneath combined net 120. Two vertices of the lower net are attached to the columns 130 a and 130 b at locations beneath (preferably 0.5 m) where the first net vertices are attached to columns 130 a and 130 b while the other two vertices of the second additional net are connected to the anchors 135.

According to another embodiment, the system comprises three or more nets. The additional net(s) are added beneath the second net (explained hereinabove) in a manner similar to the addition of the second net in relation to the first net, mutatis mutandis.

According to an embodiment of the present invention, the PCNS system is erected as follows:

-   1. The column segments are connected together forming a unified     element. -   2. The PCNS is attached to the pre-constructed attachment locations     (e.g. in the embodiment of FIGS. 3A-3B, 4A-4B, the combined net     vertex 20 a is attached to the column 30 and the other vertices to     anchors 35), obtaining an attached loose PCNS laying on the ground.

The column is then pulled to its vertical position slowly by using an auxiliary cable attached to a winch. The anchoring steel cables are tightened as the position of the vertical column progresses. This erection of the column causes pre-stressing in the combined net. Finally, all the anchoring steel cables are tightened into position. In case of two columns (e.g. FIGS. 5A-5B) both columns are erected and positioned in sequence one at a time.

Another advantage of the present invention is its redundancy, robustness and resilience. If the combined net absorbs a blast, the whole combined net system remains intact and the damaged portion is contained and amended. In case where only the fine net is damaged due to exploded munition, a piece of fine net is attached manually as a patch to the existing fine net structure to cover the hole created by the explosion (typically, a new fine net cutout the size and shape of the coarse net cell surrounding the damaged fine net portion replaces it). The patch is large enough to cover the hole and is attached to the quadrangle cell of coarse cables surrounding it. A plurality of locations on the fine cables of the fine net patch are attached to corresponding locations on the coarse cables (of the coarse net) surrounding the hole area of the fine net, by means of connecting elements (e.g. flat steel pieces as explained hereinabove). If a coarse cable is damaged, an additional coarse cable having the length larger than the damaged (missing) portion (overlapping it) is attached to the edges of the missing portion by means of connecting elements (e.g. flat steel pieces as explained hereinabove).

In case of a column being hit it is simply replaced and erected into position. Optionally the column comprises an outer layer. The outer layer is larger but similar in shape to the inner main column portion, and there is space between said inner and outer portions. The outer layer portion absorbs the blast if hit, while the inner portion remains functioning erecting the PCNS.

Optionally, the columns of the PCNS may be supported by 2, 3, 4, or more tensioned anchored steel cables, thus if one of them is hit by a blast, the other/s remain functioning.

The PCNS thus enables easy construction of a protection net and its fast assembly.

Thus, even when hit, the PCNS remains strong, robust, stable and resilient.

While some of the embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried into practice with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of a person skilled in the art, without departing from the spirit of the invention, or the scope of the claims.

REFERENCES

-   Argyris, J. H., Angelopoulos, T., and Bichat, B., “A General Method     for the Shape Finding of Lightweight Tension Structures”, Computer     Methods in Applied Mechanics and Engineering, 3, 135-149, 1974. -   Haber, R. B., and Abel, J. F., “Initial Equilibrium Solution Method     for Cable Reinforced Membranes. Part 1—Formulation”, Computer     Methods in Applied Mechanics and Engineering, 30, 263-284, 1982. -   Otto, Frei (editor), Tensile Structures, MIT Press, Cambridge,     Mass. 1973. Schek, H. J., “The force density method for form finding     and computation of general networks”, Computer Methods in Applied     Mechanics and Engineering, 3, 1974, pp 115-134. -   Siev, A., and Eidelman, J.,“Stress Analysis of Prestressed Suspended     Roofs”, Proc. ASCE, 90, ST4, pp. 103-121, August 1964. -   Zienkiewicz, O. C., The Finite Element Method, 3 rd edition,     McGraw-Hill, N.Y., 1977. 

1. A combined net structure comprising: a non-planar coarse net with a grid-like structure comprising a plurality of coarse cables wherein longitudinal coarse cables intersect with latitudinal coarse cables to form a plurality of coarse cells; cutouts of a fine net attached to said coarse net, wherein said fine net comprises a plurality of adjacent fine cables; wherein each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points, wherein said fine net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of said fine quadrangular cells.
 2. The combined net structure according to claim 1, wherein each fine net cutout is substantially coextensive in shape with one or more coarse cells.
 3. The combined net structure according to claim 2, wherein all the coarse cells are attached to fine net cutouts.
 4. The combined net structure according to claim 2, wherein the fine net cutouts are connected to the coarse net such that portions of a fine cable of said fine net cutouts are attached to corresponding portions of a coarse cable of the coarse net by means of connecting elements that hold said fine cable and said coarse cable together.
 5. The combined net structure according to claim 1, wherein the coarse net further comprises connecting elements that connect the intersecting longitudinal coarse cables with the latitudinal coarse cables at the intersecting points.
 6. The combined net structure according to claim 1, wherein the fine quadrangular cells are square or rhombic cells.
 7. The combined net structure according to claim 1, wherein the distances between two adjacent attachment points of two adjacent non-edge fine cables are substantially the same; and wherein the imaginary line which bisects and is perpendicular to the imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables passes through an attachment point of one of said two adjacent non-edge fine cables with its other adjacent fine cable.
 8. The combined net structure according to claim 1, further comprising one or more edge cables attached to the perimeter of the coarse net.
 9. The combined net structure according to claim 8, wherein the diameter of the edge cables is between 15 mm and 25 mm.
 10. The combined net structure according to claim 1, wherein the diameter of the coarse cables is between 5 mm and 10 mm.
 11. The combined net structure according to claim 1, wherein the diameter of the fine cables is between 3 mm and 6 mm.
 12. The combined net structure according to claim 6, wherein the square or rhombic cell diagonals are between 20 mm and 50 mm.
 13. The combined net structure according to claim 1, wherein the longitudinal coarse cables and the latitudinal coarse cables have predetermined lengths and are attached to each other at pre-calculated locations marked along their lengths.
 14. The combined net structure according to claim 13, wherein the predetermined lengths are such that the coarse net formed comprises a 3-dimensional structure.
 15. The combined net structure according to claim 6, wherein an imaginary line connecting two adjacent attachment points of two adjacent non-edge fine cables is parallel to the longitudinal coarse cables or to the latitudinal coarse cables.
 16. A system comprising: at least one column; the combined net structure according to claim 1; plurality of anchors; wherein the net is attached to said column and to said plurality of anchors.
 17. The system according to claim 16, wherein the combined net structure is quadrangular and one of its vertices is attached to the column, and wherein said system comprises three anchors and three vertices of said combined net structure are each attached to one of said anchors.
 18. The system according to claim 16, wherein the column is height adjustable.
 19. The system according to claim 16, wherein the anchors are concrete blocks.
 20. The system according to claim 16, wherein the system comprises one or more additional combined net structures, each of the one or more additional combined net structures comprising: a non-planar coarse net with a grid-like structure comprising a plurality of coarse cables wherein longitudinal coarse cables intersect with latitudinal coarse cables to form a plurality of coarse cells; cutouts of a fine net attached to said coarse net, wherein said fine net comprises a plurality of adjacent fine cables; wherein each non-edge fine cable is attached to two adjacent fine cables on each of its sides at a plurality of locations along their lengths forming attachment points, wherein said fine net is arranged in a form of an array of fine quadrangular cells with said attachment points constituting the vertices of said fine quadrangular cells; wherein the one or more additional combined net structures are attached to the column and to the plurality of anchors.
 21. The system according to claim 20, wherein the one or more additional combined net structures are quadrangular; wherein one of the one or more additional combined net structure vertices is attached to the column and the other one or more additional combined net structure vertices are attached to the anchors.
 22. The system according to claim 16, comprising two columns and two anchors; wherein the combined net structure is quadrangular comprising a first vertex, a second vertex, a third vertex and a fourth vertex; wherein said first vertex is attached to a first column and said second vertex is opposite to said first vertex and is attached to a second column, and wherein said third vertex and fourth vertex are each attached to one of said two anchors.
 23. The system according to claim 22, further comprising one or more additional quadrangular combined net structures, two columns and two anchors; wherein each of said one or more additional combined net structures is quadrangular and comprises a first vertex, a second vertex, a third vertex and a fourth vertex; wherein the one or more additional quadrangular combined net structures first vertex is attached to the column; and wherein the one or more additional quadrangular combined net structures second vertex is opposite to said first vertex and is attached to a second column; and wherein said third vertex and fourth vertex of said one or more additional quadrangular combined net structures are each attached to one of said two anchors.
 24. A system comprising: two intersecting arc structures; a combined net structure according to claim 1; wherein the combined net structure is spread over said two intersecting arc structures. 